Variables are things that can change. Variables include anything that might affect the results of the experiment. The variables in the cartoon diagram might be the shoes the boy is wearing, his clothes, the stick he is holding and the rope he is balancing on. Lighting and any air circulation would also have to be considered. Things you want to stay the same during the entire experiment are called controlled variables.
A cause/effect investigation has two changing variables, an independent variable and a dependent variable. The independent variable in an investigation is the instigator, the action variable that is expected to cause some change or reaction in the dependent variable.
In the diagram, any action of the hand holding the end of the rope can cause a change in the balancing time of the tightrope walker.
Remember: The objective of cause/effect investigations is to find out how changes in an independent variable affects a dependent variable.
Science Process Skill: Identifying variables in a cause/effect investigation